The present invention relates to a device designed to test the sensory nerve function of a patient who is suspected of having or has had sensory nerve damage and to compare the results to data obtained from normal, healthy subjects. Such sensory dysfunction is known to occur due to (1) trauma affecting the continuity of nerve fibers, (2) disease processes including leprosy, diabetes, multiple sclerosis, and (3) other diseases resulting in diminished nerve conductivity; and nerve compression syndromes. The data gained from evaluation with said monofilaments provides an indication of the degree to which nerve damage has progressed and/or the degree to which recovery has occurred. Data thus obtained can be used to determine appropriate medical and/or surgical treatments to alleviate nerve compression or other causes of interference. Data can also be utilized in assessing the success of therapies and therapeutic modalities directed towards aiding in the restoration of nerve function or adaptation to nerve dysfunction. The readings provide an indication of the degree of damage to the patient's sensory nerves and/or a measure of recovery from damage to the patient's sensory nerves.
Filament testing has long been used as a sensitive monitoring means for evaluation peripheral nerve function of a patient. In the 1800's, the focus of peripheral nerve testing of the hands was carried out in a study of normal physiology using horse hairs as the filaments. In the late 1950's, it was determined that a broader range of filament forces were needed than those available with horse hairs to refine the filament method for peripheral nerve testing. Thus, J. Semmes and S. Weinstein developed and published results of testing cutaneous sensory perception using nylon monofilament rods of varied diameters and consistent tips and further published methods of using those rods to apply force. The nylon filaments were affixed to plastic rods (or "filament handles") which were cut to the approximate length of a pencil for ease of handling and comfortable fit in the therapist's hand. The devices were known as "aesthiometers". The advantage of these new filaments, when affixed to a plastic rod, was their ease of handling and their ability to create a range of testing values by varying the diameter of the filament affixed to a rod. These monofilaments attached to plastic rods with glue, came to be know as "Semmes-Weinstein monofilaments" and became the standard means for repeatable testing and measurement of the threshold of cutaneous sensory perception.
The standard Semmes-Weinstein approach suffered from the fact that it required a set of twenty (20) different monofilament rods of varied diameters in order to provide an effective diagnostic technique. Each nylon monofilament was about 38 mm in length and had diameters selected to correspond to Log (10.times.force in mg) of forces ranging from 4 mg (the lowest) to 447 grams (the highest). Furthermore, virtually all Semmes-Weinstein devices employed nylon monofilaments and, nylon was found to suffer from certain drawbacks which reduced the overall efficiency of the cutaneous sensory perception-measuring device.
The proper force for determining the patient's sensory perception is obtained at the moment the monofilament bends. The fragile nature of the nylon filament requires that it be carefully handled and stored. If the monofilament is misused or mishandled, a non-elastic deformation or kink can occur. Once such a kink occurs, the standard predictable moment of force required to form a uniform bend in order to make a peripheral nerve function determination is lost. Also, properties of nylon are subject to change with climatic changes which further reduces the predictability of the force required to cause the nylon monofilament to bend. Still another impediment, as stated above, is that the diagnostician, in order to perform a complete diagnosis, using the Semmes-Weinstein approach, had to carry twenty (20) monofilaments of varying diameters at all times.
A variety of handle designs have been considered the past decades in an attempt to provide a more convenient evaluation device. These designs include a single handle having five (5) monofilaments attached thereto and radiating therefrom and which rotate on the handle by means of a screw which tightens and loosens the monofilament rack on the handle (See: U.S. Pat. No. 5,381,806, Weinstein, et al.) This design was awkward to use when attempting to apply force against those areas of skin which may be difficult to reach such as the palm of a hand when that hand is held in a fist position or any other body parts that may be contracted in abnormal postures because, in attempting to contact the skin with only one point of a single filament, contact is often made by the non-selected filaments with adjacent body parts thereby negating the single stimulus response of the patient. These multi-filament handles also used nylon filaments which have the disadvantages noted above and additionally, requires that the entire set be replaced when even a single monofilament becomes unusable because of deformation or failure.
More recently, the use of alternative filament materials such as steel, were employed in the belief that they would enhance the accuracy of pressure aesthiometers by providing a force which is consistent over time and which is capable of providing a consistent footprint of area of stimulus. The steel wire pressure aesthesiometer presented by Kanatani in U.S. Pat. No. 4,313,446 provided an instrument purportedly capable of delivering such variable forces but had the distinct disadvantage of utilizing an exposed filament which was subject to deformation if not properly stored, and which required the interchange of filaments of varying diameters to provide for a full range of testing. Furthermore, steel has limited elastic properties and therefore is subject to inelastic bending. In such cases, the accuracy of force delivery is compromised resulting in a deviation from known clinical protocols.
The Kanatani design further required a deflection gauge upon which the diagnostician had to rely in order to achieve the desired range of filament deflection required to apply a promised force in grams of pressures. From the table given in FIG. 9 of the Kanatani patent (U.S. Pat. No. 4,313,446), it can be seen that in the smaller diameter filaments, a variance in deflection as small as 2.5 mm results in a 175% increase in the stress applied as measured in grams per square millimeter and a deflection variance of 10 mm will result in a 235% increase in the stress applied as measured in grams per square millimeter.
Thus, a major clinical disadvantage of the design proposed by Kanatani is that an evaluator must be ever alert to the area being tested and to the graph attached to the instrument indicating the degree of deflection. Tests of cutaneous sensory perception require care and precision to perform accurately and attention to the area of applied force is required particularly with persons who have known sensory dysfunction. Alteration of sympathetic function including sudomotor, vasomotor and pilomotor function, often result in trophic changes in affected areas. The result of these trophic changes may include loss of sweat patterns and skin dryness due to loss of the normal nutritive process of the skin. Skin may become thin and smooth and testing must be performed with caution and attention to prevent filaments from sliding or skipping on the skin which, if it occurs, will negate the single footprint stimulus required for objective evaluation. Control of the variables involved in testing to the extent possible reduces the subjectivity inherent in evaluation of the perception of a stimulus. Monitoring both the area and application of the stimulus and the instruments' deflection graph is clinically undesirable. In addition, the Kanatani instrument also required a bulky protective carrier and was not designed to provide convenience of use.
Other existing apparatuses used for the same and similar purpose as the Semmes-Weinstein devices employed a plurality of nylon filaments grouped into holders which provide multiple forces depending upon the filament chosen. These devices are awkward to use and bulky to store and carry, and do not permit truly accurate peripheral nerve testing of patients who have or who are recovering from sensory nerve damage. A substantially complete description of the art to which this present invention pertains can be found in "Somatosensory Occupational Therapy Association, Inc., Bethesda, Md. in 1977.
In spite of the various advances occurring through the years, as herein described, a clear need still exists for a new and improved monofilament sensory device which overcomes the significant deficiencies in the prior art which is readily portable and is capable of creating reproducible results irrespective of circumstances. It is toward these goals that the present invention is directed.
It is thus an object of the present invention to provide a hand-held single-point sensory evaluation device which eliminates the need for inventorying multiple evaluation tools, provides a consistent calibrated force over the entire range of desired testing, is clinically useful and substantially reduces the subjectivity in the evaluation of sensory nerve function.
A further object of the present invention is to provide a single tool which is easily held in the palm of the hand and which provides a multiple selection of precise forces to be applied to a patient utilizing a single monofilament, braid or wire.
A still further object of the present invention, is to provide unique means and methods for determining a precisely calibrated force or pressure over an entire continuous range not limited to pre-selected end point values at the end of the monofilament when that monofilament is pressed against the skin of the test subject until the filament bows.
Still another object of the present invention is to provide a single handheld instrument that reduces the variables involved in determining the calibrated force application to the single variable of filament deflection as a factor of force or pressure.
A still further object of the present invention is to provide an instrument that complies with clinically valid constructs whereby the instrument delivers a sensory filament at a 90-degree angle to the handle and can be further modified to deliver "ergonomically sensitive" angles for applications not yet clinically validated.
These and still further objects, as shall hereinafter appear, are readily fulfilled by the present invention in a remarkably unexpected manner as will be readily discerned from the following detailed description of exemplary embodiments thereof especially when read in conjunction with the accompanying drawings in which like parts bear like indicia throughout the several views.